1. Field of the Invention
This invention relates to a process for producing with high selectivity 5-vinyl2-norbornene (hereinafter referred to as VNB) and/or 3a, 4,7,7a-tetrahydroindene (hereinafter referred to as THI) by the Diels-Alder reaction between butadiene and cyclopentadiene.
2. Description of the Prior Art
VNB can be isomerized to produce its isomer 5-ethylidene-2-norbornene (hereinafter referred to as ENB) which is one of the third components useful for the so-called EPT rubber.
THI can be converted to a higher polymer by the Friedel-Crafts reaction or the Diels-Alder reaction and the resultant high polymer is useful as a petroleum resin. Further, an epoxidized THI is promising as a kind of epoxy resin.
These VNB and THI can be produced by the Diels-Alder reaction between butadiene-1,3 and cyclopentadiene. However, the selectivity for VNB and/or THI is not satisfactory. In the Diels-Alder reaction between butadiene-1,3 and cyclopentadiene, there are formed, beside VNB and THI, both of which are 1: 1 adducts, 4-vinylcyclohexene and 1,5-cyclooctadiene by the dimerization of butadiene-1,3, dicyclopentadiene by the dimerization of cyclopentadiene, and, further, trimers, cotrimers and even higher polymers.
Cyclopentadiene and dicyclopentadiene are in the reversible equilibrium relation that at 130.degree. C. or more, dicyclopentadiene is apt to be converted into cyclopentadiene, while at less than 130.degree. C., cyclopentadiene is apt to be converted into dicyclopentadiene. Further, it is known that the amount of THI formed directly from butadiene 1,3 and cyclopentadiene is less than that formed by the rearrangement of VNB which has been produced by the reaction of butadiene-1,3 and cyclopentadiene [T. Maeda, M. Muranaka, S. Hamanaka and M. Ogawa, Journal of Chemical Society of Japan, 1974 (8), 1587-9; S. Iwase, M. Nakata, S. Hamanaka, and M. Ogawa, Bulletin of Chemical Society of Japan, Vol. 49, (7) 2017-8 (1976)]. Accordingly, VNB is formed in a major amount in the earlier stage or reaction between butadiene-1,3 and cyclopentadiene or under mild reaction conditions, while the total amount of THI formed is increased in the later stage of the reaction or under severe reaction conditions because the rearrangement of VNB to THI is increased.
The use of a hydrocarbon having 5 to 7 carbon atoms or an ester of a monocarboxylic acid, said acid having 2 to 7 carbon atoms, in the Diels-Alder reaction between butadiene-1,3 and cyclopentadiene has been disclosed in Japanese Patent Publication No. 25,665/74.
The present inventers have conducted extensive research on the effect of a solvent on the reaction for producing VNB and THI from butadiene-1,3 and cyclopentadiene, and as a result, have found that the overall yield of VNB and THI is proportional to the molecular refraction R.sub.D of the solvent.